test: add test for invalid value

Author: kenjis

tests/system/HTTP/IncomingRequestTest.php

@@ -17,6 +17,7 @@
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\App;
 use Generator;
+use InvalidArgumentException;
 use TypeError;
 
 /**
@@ -649,6 +650,16 @@ public function testIsHTTPMethodUpperCase(string $value)
         $this->assertTrue($request->is($value));
     }
 
+    public function testIsInvalidValue()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Unknown value: invalid');
+
+        $request = $this->request->withMethod('GET');
+
+        $request->is('invalid');
+    }
+
     public function testIsJson()
     {
         $request = $this->request->setHeader('Content-Type', 'application/json');